The present invention concerns an analysis method and a cuvette for performing this analysis. Specifically the invention concerns a method for determination of haemoglobin in undiluted whole blood and a disposable cuvette which can be used in this determination.
A disposable cuvette for sampling a fluid, mixing the sample with a reagent and directly making optical analyses of the sample mixed with the reagent is previously known from U.S. Pat. No. 4,088,448. This known cuvette has several advantages as it i.a. simplifies the sampling procedure, reduces the number of utensils and considerably improves the accuracy of analysis by making the analysing procedure independent of the operating technique of the operator making the analysis. A cuvette construction based on the same principle and with improved flow characteristics is disclosed in the U.S. Pat. No. 5,674,457.
A disposable cuvette developed according to these patents is currently widely used for haemoglobin measurement(Hb determination) of undiluted whole blood. To this end the cuvette cavity has been pre-treated with a reagent, such that when a blood sample is drawn into the cuvette, the walls of the red blood cells are disintegrated and a chemical reaction is initiated. The result of the reaction allows Hb determination by absorption measurement directly through the transparent walls of the cuvette which, in the measuring zone, also called the optical window, has a predetermined and accurately defined distance between the inner surfaces of the opposing planar walls. The measurement method is based on a modified azidmethemoglobin method according to Vanzetti, G., Am.J. Lab.and Clin. Med. 67, 116 (1966).
The spectophotometric measurements are made at 570 and 880 nm. This quantitative measurement method based on dry chemistry has met with considerable success as can be seen in e.g. the article by von Schenck et al in Clinical Chemistry, vol 32, No 3, 1986 as the method gives equal or even superior results in comparison with the results obtained with standardised wet methods for the determination of Hb. The reagent used is comprised of sodium deoxycholate which hemolyses the red blood cells, sodium azide and sodium nitrite, which converts haemoglobin to azidmethemoglobin.
Due to the hygroscopic properties of the reagents used, the shelf life is limited and the storage of the cuvettes in sealed packages including a drying agent is required. Even more troublesome is the fact that, in climates with high humidity, the cuvette has to be used within a few minutes after the removal from the package, as otherwise the reagents will be destroyed and the measurement will be inaccurate and thus useless.
An object of the present invention is to provide a rapid, quantitative method for the determination of hemoglobin in whole blood.
A second object is to provide a method for the determination of hemoglobin in whole blood, which may be performed in a disposable microcuvette.
A third object is to provide a microcuvette for the determination of hemoglobin in undiluted, whole blood in which method the problems originating from the hygroscopic properties of the reagents are eliminated.
Other objects will be apparent from the following description and the accompanying claims.
In accordance with the present invention a method for providing such a hemoglobin determination comprises the steps of introducing a sample of undiluted whole blood by capillary action into a disposable microcuvette having at least one cavity for receiving the sample. The cavity includes a dry essentially non-hygroscopic hemolysing agent, which is dissolved by the blood, hemolyses the red blood cells and releases the haemoglobin contained in the blood cells. A first absorption measurement at a wavelength range 490-520 nm is then performed directly on the sample in the microcuvette, and a second absorption measurement is performed to compensate for background interference.
It has thus unexpectedly been found that quantitative determinations of haemoglobin can be performed without the chemical reagents sodium azide and sodium nitrite mentioned above. More specifically, it has been found that quantitative determinations may be performed directly on the hemolysed blood provided that an appropriate hemolysing agent or a mixture thereof is selected.
In accordance with the present invention it has thus been found that the hygroscopic reagents can be eliminated. Furthermore, it has been found that the time for obtaining the analytical determination may be reduced. As the analyses are performed in large amounts in e.g. hospitals and blood banks, the time aspect is important.